In my prior patent, U.S. Pat. No. 4,264,990, I explained the problems with prior art mammary prostheses and disclosed and claimed mammary prostheses that have a unique rigid back to prevent hardening by scar contracture. I have now invented another mammary prosthesis that will resist scar contracture and which will be easier to implant than those described in the above noted patent. In U.S. Pat. No. 3,366,975, a foamed coating over the surface of the mammary prosthesis is suggested to promote ingrowth of tissue and attachment of tissue to the surface of the prosthesis. According to the invention disclosed in this application, the surface of the prosthesis is provided with a plurality of rigid protuberances but in such a way to avoid tissue ingrowth and attachment. It should further be understood that this invention does not simply comprise providing a rough surface on the prosthesis but a pattern of projections especially arranged and spaced to hold the scar tissue from the surface of the implant envelope thus providing a space into which the envelope can be stretched. In this way, the implant can change shape even when the scar tissue has contracted.